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ALUMINUM MELTING AND METAL QUALITY PROCESSING TECHNOLOGY
FOR CONTINUOUS HIGH QUALITY CASTINGS
Copyright©2001 American Foundry Society
ABSTRACT
Scott Kennedy
Inductotherm International
Aluminum Group
The aluminum industry has moved more towards complete integrated melt and metal treatment systems as a total process in
order to provide continuous quality metal for casting operations. In years past new aluminum casting plant layouts were
approached by purchasing a number of system requirements such as melting, degassing, filtering and metal transfer from a
number of suppliers. Today high technology equipment OEM’s are offering complete turnkey systems for individually
engineered casting needs. This in turn takes a burden off the foundry engineers to spend more time in careful selection of the
critical casting equipment to achieve high quality aluminum parts. Eliminating metal quality issues from the equation allows
for a smooth start-up transition with a reduced number of equipment suppliers. This paper will address the melting system
concept approach allowing for careful consideration for new plant casting facilities.
INTRODUCTION
The world market growth in aluminum castings has increased dramatically over the past thirty years. In conjunction with this
growth increased emphasis on casting quality and energy conservation has been key issues. The world energy problems have
resulted in increased costs and reduced availability of resources. Aluminum processing equipment that reduces energy
consumption per ton cast is of prime importance to all foundries in today’s competitive market. Environmental mandates
also are an important factor on more efficient methods of aluminum melting and processing. The demand to provide high
quality castings has caused aluminum foundries to look at more integrated melting and metal treatment process systems to
provide continuous controlled metal quality output. This paper will address the melting equipment available in the world
market with inclusion of in line metal treatment systems.
ADDRESSING METAL QUALITY ISSUES
As the aluminum foundry industry grows it is necessary to return to the basic roots. Achieving high metal quality is not a
new art it is returning to the basics of controlling the process. Pick up a Kaiser Casting book from 1945 and review metal
treatment practices and they differ very slightly from today. So why do so many foundries constantly deal with metal quality
problems, the answer goes back to the written word of our foundry pioneers. We have become sloppy and careless on how
the metal process is treated. The new foundry personnel are not being taught the basics of good foundry practices.
Management must pass on valuable training on how to handle the fastest growing casting metal in the world today.
MELTING EQUIPMENT
Melting equipment offered today must meet a number of important criteria including energy efficiency, metal loss, metal
quality and of course be worker friendly. Many of the furnace concepts being offered are not new like many of us are led to
believe. Furnace designs such as stack charge melters and furnaces with regenerative burners have been around for over
thirty years. So we ask ourselves why did we ignore them, but the answer is quite simple we are driven by profit not energy
conservation. The idea of us paying three times the cost for a furnace to use reduced energy ten or twenty years ago was not
a practical investment. The European and Asian market was forced into energy conservation more than a decade before
North and South American. Since the energy and environmental situation will only worsen worldwide the future selection of
furnace equipment will be more costly up front, but return on investment due to energy costs and environmental restrictions
will be more attractive. We therefore need to understand the equipment available to the aluminum casting market in order to
make wise investment decisions for future casting growth.

The melting equipment available in today’s market includes crucibles, reverbs, dry hearths, induction, and stack melters.
Each of these categories has a number of different approaches offered.
CRUCIBLE FURNACE
Many small jobbing foundries that melt a number of different alloys use these furnaces. The crucible furnaces are also
popular in holding applications such as at die cast stations and used in many foundries as metal transfer ladles. The crucible
concept was the backbone to the start of the foundry industry. They are the least expensive in purchase price of the melting
furnaces for the small volume user. These furnaces are available in fossil fuel, electric resistance and induction.
GAS FIRED CRUCIBLES
The furnace consists of an outer steel shell with 6” to 9” of insulation with a silicon carbide crucible set in the center.
Today’s gas crucible furnaces are normally heated with compact package burners or high velocity burners. Unfortunately,
they are the least efficient method of melting due to the compact combustion space and price restrictions on recuperative
burners. The use of proportioning burners with high turn down and good insulation can improve efficiency from the old
premix approach.
1000# Gas Crucible Furnace
1000# GAS CRUCIBLE FURNACE
ELECTRIC RESISTANCE CRUCIBLES
The electric resistance crucible furnace mostly commonly heated with metallic elements or silicon carbide. These furnaces
are well insulated with ceramic fiber and are available in a number of configurations such as stationary, tilt and bail transfer.
The life of the heating elements are depending on the gauge of the element and operating temperature. The heavier gauge
elements have demonstrated two to three times the life of the thin gauge element in melting applications. These furnaces are
also commonly used in holding applications at the casting machine.

150kw/2000# Electric Crucible Furnace Line
DIRECT HEAT CRUCIBLE FURNACE
This is a new design concept, which transfers the electrical energy directly into the crucible resulting in the highest efficiency
available in crucible melting. Since the majority of electrical energy (upwards of 90%) goes into the crucible all other
furnace components stay cool. Due to low furnace losses air-cooling is all that is required for the induction coil. Quick
melting is achieved without the temperature over shoot commonly found in crucible furnaces.
Direct Heat Crucible Furnace

DRY HEARTH FURNACES
The dry hearth furnace is popular choice for foundries that re-melt castings with ferrous inserts or screens. They also provide
flexibility in melting all forms of scrap and large sows and T-bars. The furnace design allows all melting to be done on a
sloping hearth from where the metal flows into a separate hold chamber. This furnace eliminates the chance of metal
explosions caused by moisture present in the charge material being directly placed into the molten metal. Since both the melt
chamber and hold chamber are separately controlled it allows for close metal temperature control. The furnace also holds
half the metal capacity of traditional wet bath reverbs and the melt chamber can be put on idle during non-production hours.
The more efficient dry hearth designs incorporate roof radiant burners eliminating flame impingement on the metal reducing
metal loss. These furnaces typical use conventional burners but also can be provided with regenerative burners.
2000#/Hr. Dry Hearth Furnace
Radiant Roof Burners

WET BATH REVERBS
The wet bath reverb melts the metal by direct charge into the bath. They can also include a sow hearth for placing sows, tbars,
or ingot stacks for preheating prior to charging into the bath. Since their ratio of melt to hold runs about 10 to 1 side
well re-circulation on the larger furnace is quite common improving melt efficiency and temperature uniformity. This to date
has been the most common furnace approach in the large casting foundry. The burners used have typically been conventional
with high velocity or radiant roof design. The applications of regenerative burners are becoming more common with the
increasing energy costs. The regenerative burners can in some cases increase the base cost of the furnace by 60 to 80%.
These furnaces are also good application for chip melting systems and attaching to launder integrated casting lines.
4000#/Hr. Gas Wet Bath Reverb With Sow Hearth
BARREL WET BATH REVERB FURNACE
The barrel wet bath-melting furnace has been around for a number of years. It is used mainly as a central melt furnace for
fast and efficient metal transfer to bull ladles. Today’s barrel furnace use high velocity burners for improved melt efficiency
and are offered with sow preheat hearths. Direct scrap charge can be placed in the end well. The circular locking high
alumina brick construction provides good refractory furnace life.

5000#/Hr. Gas Barrel Furnace
ELECTRIC REVERB FURNACE
The electric reverb was brought into the market in the early 70’s during the Midwest energy crisis. The furnace
was heated with silicon carbide elements and was offered in sizes upward 3000#/Hr. The design is still popular in
high quality casting applications such as the electric motor market. Where melt rates are required in excess of
crucible melting, this furnace style is a good option.
1200#/Hr. Electric Reverb

CORELESS INDUCTION
The coreless induction furnace has been a very popular melt concept from the small jobbing foundries to the large remelt
shops. Low to medium frequency induction coils transfer energy directly into the melt. The small foundries that
batch melt a variety of alloys find these furnaces fast and efficient. The large foundries use them in scrap and chip
melting applications. They are the most efficient way to melt chips with upwards of a 98% yield.
Coreless Induction
STACK MELTERS
The stack melter has had more presence to date in the Europe and Asia market due to high-energy costs. The North
American market is paying a lot more attention to this efficient method of melting. The original stack or tower melter
accepts all charges through the exhaust stack. The heat normally exhausted is used to pre-heat the scrap or ingot being
charged reducing the fuel usage per pound melted. The drawback of these furnaces is the inability to melt sows or t-bars, but
a stack melt dry hearth furnace is available that can accept all the alternate charge materials.

2000#/Hr. Stack Melter
4000#/Hr. Stack Charge Dry Hearth Furnace

CHART OF FURNACE EFFICIENCIES
TYPE OF FURNACE RANGE OF BTU’S/POUND RANGE OF METAL LOSS
GAS CRUCIBLE 2500 – 4000 1 - 3%
ELECTRIC CRUCIBLE 716 - 887 1 – 1.5%
ACUTRAK DIRECT HEAT 560 - 590 .5 – 1%
CORELESS INDUCTION 785 - 887 1 – 1.5%
DRY HEARTH 1500 – 2000 2 – 4%
WET BATH REVERB 1500 – 1800 1.5 – 3%
BARREL MELTER 1500 – 1800 1.5 – 3%
STACK MELTER 1100 – 1300 1 – 2%
STACK DRY HEARTH MELTER 1200 – 1400 1.5 – 3%
REGENERATIVE WET BATH 1000 – 1300 1.5 – 3%
ELECTRIC REVERB 716 – 853 1 – 1.5%
*The use of regenerative burners in the wet bath and dry hearth furnaces can result in an average of 500 BTU’s per
pound savings.
METAL PROCESS SYSTEMS
The control of the casting process starts from the quality of metal being charged to how we treat the metal in its final stage
before casting. From the small jobbing foundry to the large automotive casting facility an integrated melt and process system
is needed to ensure metal control. The training of foundry personnel in the basics of metal handling and treatment on an
ongoing basis is very important. In over 70% of casting shops the foundry personnel have no real understanding of the basics
such as why we flux, degas, grain refine or modify aluminum alloys. There are no good excuses for this with the information
that is so freely available through AFS and other organizations.
SMALL JOBBING FOUNDRIES
An up to date continuous crucible melting approach would include an ingot charger with a pivotal rotary degasser followed
by an automatic ladle. Grain refiners and modifiers would be introduced by hand to meet desired metal quality. Filtering in
this process is usually accomplished by flux injection through the degasser or by hand application.
In a batch melt system the furnace would be loaded and after complete meltdown and metal at temperature the degassing and
fluxing process would take place. The crucible melt shop does not lend itself to the advantages of more integrated metal
treatment controls due to furnace size and numbers of alloys. Once a foundry gets into high melt rate of singular alloys a
review of melt systems should be considered.
Crucible Auto Ladle Station Ingot Charger

MEDIUM SIZE MELT SHOPS
The medium size foundry has a number of systems to choose from in control of metal quality. The use of rotary degassers
and filters allows for good metal treatment when applied correctly. Many foundries have used gate style filtering in exit
wells of melt and holding furnaces. The foundry management likes the ability to change these filters without draining the
furnace. Unfortunately the majority of these applications do not assure proper placement of the filter causing metal to bypass
the filter media resulting in no metal cleaning. The other problem is the filters are not probably preheated and block over
50% when placed into the metal. The result is a significant temperature drop between one side and the other of the filter.
This has an adverse effect by causing the melt chamber to run excessively hot resulting in increased oxidation and hydrogen
absorption into the metal. A solution to this problem is to use a silicon carbide filter box in the well, which provides a lot of
surface area and reduced metal temperature gradient. Since all sides and bottom are filter media they assure complete metal
filtering with no bypass. When the filter box starts to block or accidentally broken it can be replaced within 20 to 30 minutes.
Automatic ladling should also be considered when possible to assure continuously pour rates.
4000#/Hr. Wet Bath Reverb With Degassing And Filtration

Ladling Furnace With Inset Silicon Carbide Filter Boxes
LARGE FOUNDRY INTEGRATED SYSTEMS
Today’s large foundries have the option of laying out the casting shop for complete continuous metal control. The
availability of efficient melting systems connected to heated launder, degassing, filtering and holding furnaces allows for
constant high metal quality castings. The ability to melt and cast without any manual metal transfer over the floor can be
achieved with a complete integrated melt facility.
DEGASSING FURNACE
The degassing furnace is electric heated and can be installed with an inlet and outlet rotary degassing station. This approach
allows for independent degassing outside of the melt furnace achieving controllable levels downwards of .07cc/100gm.
hydrogen content. The levels of hydrogen can be increased or decreased depending on your casting requirements with the
use of inert gas such as nitrogen and argon with proper RPM and dispersion head design.
HEATED LAUNDER SYSTEMS
The intent of high efficiency electric heated launder systems allows us to connect from the melter to the casting furnace
without subjecting the metal to unwanted turbulence. This closed loop approach completely changes the conditions inherent
in a standard aluminum foundry. In some of the modern installations it is hard to detect that liquid metal exists in the facility.
The melt furnace can be connected directly to the launder or the metal can be transferred by pressure pump well to the
launder with laser level control. The launders normally have 1-1/2KW hooked up per linear foot and have nitrogen purge to
minimize metal oxidation. Since they are very well insulated the power usage is minimal. The launder system allows for a
modular concept allowing for additional casting cells to be added as the foundry grows. Some plants will have as many as 20
to 30 casting stations fed by a launder system.

FILTRATION FURNACE
The electric heated filtration furnace assures all metal going though the line is filtered. Different from the gate filter approach
the use of filter bowl seating makes for a sure seal between incoming and outgoing metal. The filter furnace allows for up to
12,000 lbs. per hour of treated metal and an average of two weeks prior to filter replacement. The furnace has a typical input
of 30K to maintain metal temperature.
CASTING FURNACE
The launder system will eventually feed a number of electric heated holding/casting furnaces. Since the launder can supply a
continuous source of metal the casting furnace does not have to hold a large capacity of metal reducing the space needed at
each casting station. The furnace wells can be designed to accommodate either ladles or pumps.
4000#/Hr. Lost Foam Automated Line With Complete Metal Treatment System And Casting Furnace. The
Casting Line Provides Metal Gas Levels Of .10cc/100gm. And Inclusion Removals Of 80% Or More.

Electric Degassing Furnace Connected To Outlet Of 4000#/Hr. Melter
30 Kw Filter Furnace Connected To The Launder Line

12,000# Electric Ladling Furnace Completes The Integrated Casting Line
high efficiency electric launder system for connecting system

Automated Casting Line Including Two Melters, Degassing, Filtration, Launder And Casting Furnaces
10,000#/Hr. 120,000# Hold Capacity Regenerative Melter Connected To A Complete Integrated Metal
Delivery System

Completely Automated Piston Line With Over 400 Ft. Of Electric Launder Connecting To Central Melters
With Laser Level Control And 12 Casting Cells
TOTAL INTEGRATED SYSTEM CONCEPT
A complete casting facility would have a series of melters feeding a central launder system. Metal treatment though
degassing and filtering would feed continuous high quality temperature controlled metal to each casting station. The entire
transfer system would be nitrogen purged to minimize gas and oxide pickup through the system. Automatic rod feeding for
grain refinement and modification can be an additional feature of the feed line. The integrated system concept minimizes the
chance of human error allowing for continuous high quality metal resulting in lower scrap rates and castings of high integrity.
The future high production foundries will eliminate all manual means of metal transfer increasing plant safety and metal
quality control.